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Module 1: Introduction & Regular Languages

20232m

Let NN be an NFA with nn states and let MM be the minimized DFA with mm states recognizing the same language. Which of the following is necessarily true?

(i) m≤2nm \le 2^n
(ii) n≤mn \le m
(iii) MM has one accept state
(iv) m=2nm = 2^n

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Answer

Correct Option: (i) m≤2nm \le 2^{n}

Explanation

NFA → DFA subset construction:

  • Each DFA state corresponds to a subset of NFA states.
  • With nn NFA states, there are at most 2n2^{n} subsets.
  • Hence the DFA obtained (before minimization) has ≤2n\le 2^{n} states.
  • Minimized DFA MM has m≤m \le number of subset-construction DFA states ≤2n\le 2^{n}.

So (i) is always true.

Other options:

  • (ii) n≤mn \le m is false: NFA can be exponentially smaller (e.g., language of nthn^{th} from end needs n+1n+1 NFA states but 2n2^{n} DFA states → n<mn < m sometimes, but not necessarily; sometimes DFA is smaller).
  • The converse m≥nm \ge n is not guaranteed.

Final Answer

m≤2nm \le 2^{n} → Option (i). (Minimized DFA minimal, so mm is even tighter, but certainly ≤2n\le 2^{n}.)

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